More power management updates for v4.13-rc1

 - Revert a recent change in the generic power domains (genpd)
   framework that led to regressions and turned out the be misguided
   (Rafael Wysocki).

 - Fix a recently introduced build issue in the generic power domains
   (genpd) framework (Arnd Bergmann).

 - Constify attribute_group structures in the PM core, the cpufreq
   stats code and in intel_pstate (Arvind Yadav).
Merge branches 'pm-domains', 'pm-sleep' and 'pm-cpufreq'

* pm-domains:
  PM / Domains: provide pm_genpd_poweroff_noirq() stub
  Revert "PM / Domains: Handle safely genpd_syscore_switch() call on non-genpd device"

* pm-sleep:
  PM / sleep: constify attribute_group structures

* pm-cpufreq:
  cpufreq: intel_pstate: constify attribute_group structures
  cpufreq: cpufreq_stats: constify attribute_group structures